Vanadium corrosion inhibitor

ABSTRACT

A corrosion inhibited fuel mixture includes a hydrocarbon fuel, at least one vanadium composition, and a yttrium composition. The concentration of the yttrium composition in the mixture provides at least a stoichiometric amount of yttrium for a substantially complete reaction between the yttrium and V 2  O 5  formed from the vanadium composition when the mixture is burned. The yttrium and V 2  O 5  react to form YVO 4 . One particular yttrium composition useful as a hydrocarbon fuel soluble, water stable vanadium corrosion inhibitor incorporates a yttrium ester having at least four carbon atoms and a hydrocarbon fuel soluble chelating agent that includes 2,4-pentanedi. .e.!..Iadd.o.Iaddend.ne. The complex has a molar ratio of 2,4-pentanedi. .e.!..Iadd.o.Iaddend.ne to yttrium of up to 5:1.

DESCRIPTION

This invention was made with Government support under contract numberN00014-89-C-0053 awarded by the Departmnent of the Navy. The Governmenthas certain rights in this invention.

TECHNICAL FIELD

The present invention is directed to a vanadium corrosion inhibitor,particularly a fuel soluble, water stable vanadium corrosion inhibitor.

BACKGROUND ART

Gas turbine engines serve as principle sources of power in air, marine,and industrial environments. In a gas turbine engine, air is compressedand mixed with a fuel to form a combustible fuel/air mixture. Thefuel/air mixture is then burned to produce hot exhaust gas that expandsacross a turbine to produce power. As with all heat engines, theefficiency of a gas turbine engine is related to the maximum and minimumtemperatures in its operating cycle. To increase the efficiency andperformance of such engines, therefore, it is desirable to increase thetemperature of the exhaust gas at the turbine inlet. The turbine inlettemperature of the exhaust gas in a typical gas turbine engine hasincreased from about 700° C. in the early 1950s to about 1350° C. inpresent day engines. The increase in turbine inlet temperature was madepossible by advances in metallurgy and component cooling techniques.

As a result of high turbine inlet temperatures, turbine componentsoperate under complex and demanding combinations of stress andtemperature in a high-velocity gas stream To withstand such conditions,components in the turbine, particularly the turbine blades, aretypically made from nickel-based superalloys. Extensive experience hasshown that such alloys provide good resistance to creep, fatigue, andmost types of corrosion, which are the principle degradation mechanismsin the hot sections (i.e., the combustion chamber and turbine) of gasturbine engines. The superalloys, however, are vulnerable to hotcorrosion, which causes the breakdown of the protective oxide scaleordinarily present on these materials. The breakdown of the protectiveoxide scale accelerates the rate of consumption of the underlyingsubstrate. Hot corrosion can be promoted by various contaminants presentin the fuel and air, such as vanadium (V) and sodium (Na).

Vanadium is not typically found in distillate fuels, such as jet fuels.Therefore, vanadium induced hot corrosion is not a major concern foraircraft gas turbine engines. Vanadium, however, often is present inresidual fuel oils, such as those used in marine and industrial gasturbines, and in some crude oils. The vanadium is usually present as aporphyrin or other organometallic complex but inorganic compounds ofvanadium also have been reported. During combustion of the fuel,vanadium reacts with oxygen to form oxides. The vanadium-oxygen systemcomprises at least four oxides, VO.V₂ O₃.V₂ O₄ (VO₂), and V₂ O₅. Thefirst three oxides are refractory materials that have melting points inexcess of 1500° C. As a result, they pass harmlessly through theturbine. V₂ O, however, has a melting point of about 670° C. Therefore.V₂ O₅ is a liquid at gas turbine operating temperatures and easilydeposits on the surfaces of hot components to cause corrosion.

Sodium vanadate forms when sodium salts, which are present in either thefuel or air (particularly in marine environments react with vanadiumoxides. The sodium vanadate phases flux the normally protective oxidescales found on nickel-based superalloys.

Early studies of vanadium hot corrosion recognized that the acceleratedoxidation associated with the presence of liquid V₂ O₅ could beattenuated if the melting point of the reaction products could be raisedabove the temperature inside a gas turbine engine. Researchers foundthat certain compounds, such as metal oxides, react with V₂ O₅ to formrefractory vanadates. To date, numerous additives have been evaluatedfor their effectiveness in inhibiting vanadium hot corrosion. Currently,magnesium-containing compounds (e.g., MgSO₄) are widely used in theindustry because they can decompose to magnesium oxide (MgO). which inturn reacts with V₂ O₅ to form magnesium vanadate (Mg₃ (VO₄) ₂).Magnesium vanadate has a melting point of 1150° C. For reasons that arenot well understood however, MgSO₄ is not particularly effective ininhibiting sodium vanadate corrosion. In addition, sulfur, such as fromsodium sulfates in the compressor and SO₂ from the fuel, greatly reducesthe effectiveness of the MgO formed from MgSO₄ because MgO reactspreferentially with the sulfur to form MgSO₄ rather than with V₂ O₅ toform magnesium vanadate.

As a result there is a need for a vanadium corrosion inhibitor that alsois effective in the presence of sulfur and against sodium vanadatecorrosion.

DISCLOSURE OF THE INVENTION

The present invention is directed to a vanadium corrosion inhibitor thatalso is effective in the presence of sulfur and against sodium vanadatecorrosion.

One aspect of the invention includes a mixture of a hydrocarbon fuel, atleast one vanadium composition, and a yttrium composition. Theconcentration of the yttrium composition in the mixture provides atleast a stoichiometric amount of yttrium for a substantially completereaction between the yttrium and V₂ O₅ formed from the vanadiumcomposition when the mixture is burned. The yttrium and V₂ O₅ react toform YVO₄.

Another aspect of the invention includes a hydrocarbon fuel soluble,water stable vanadium corrosion inhibitor that incorporates a yttriumester having at least four carbon atoms and a hydrocarbon fuel solublechelating agent that includes 2,4-pentanedi. .e.!..Iadd.o.Iaddend.ne.The complex has a molar ratio of 2,4-pentanedi. .e.!..Iadd.o.Iaddend.neto yttrium of up to 5:1.

These and other features and advantages of the present invention willbecome more apparent from the following description.

BEST MODE FOR CARRYING OUT THE INVENTION

We discovered that yttrium (Y) in the form of yttria (Y₂ O₃) and othercompounds react with V₂ O₅ to form a refractory vanadate. YVO₄. Theformation of YVO₄, which has a melting point greater than 1800° C.,effectively inhibits vanadium hot corrosion in gas turbine enginesbecause YVO₄ remains a solid at typical gas turbine operatingtemperatures. Experimental results have shown that yttrium chloride(YCl₃). which reacts with oxygen in combustion air to form Y₂ O₃. can bean effective fuel oil additive. Although YCl₃ is not soluble inhydrocarbon fuels, it is soluble in the water that can be present inmany residual fuel oils and crude oils. Even so, using YCl₃ as avanadium corrosion inhibitor can present practical problems. Otheryttrium compositions, however, are soluble in hydrocarbon fuels andstable in the presence of water, making them potentially more flexiblethan YCl₃. As a result, this application focusses primarily on fuelsoluble yttrium compositions.

We found that a fuel soluble, water stable inhibitor can be made byreacting a yttrium ester with a fuel soluble chelating agent to form anester/chelating agent complex. In addition to yttrium, the ester shouldcomprise at least four carbon atoms. Preferably, the ester will comprisefour to twelve carbon atoms and, most preferably, will be yttriumoctonate or yttrium 2-ethyl hexanoate. These esters are preferredbecause they are oil soluble, hydrolytically stable, and are readilyavailable. The chelating agent should be soluble in the types ofhydrocarbon fuels most prone to be associated with vanadium corrosion,such as residual fuel oils or crude oils, and should be reactive withvanadium. The chelating agent that meets these criteria is2,4-pentanedi. .e.!..Iadd.o.Iaddend.ne.

The amount of yttrium ester and chelating agent reacted to form thecomplex can vary over a broad range. For example, the ester/chelatingagent complex may comprise up to five moles of chelating agent per moleof yttrium in the ester. Preferably, the complex will comprise two tothree moles of chelating agent per mole of yttrium. Most preferably, thecomplex will comprise three moles of chelating agent per mole ofyttrium. The reaction to form the ester/chelating agent complex may takeplace in a suitable hydrocarbon solvent such as Jet A fuel. No. 2heating oil (diesel fuel). or another suitable hydrocarbon. For example,50 g. of yttrium.sub.(111) 2-ethyl hexanoate, available from AldrichChemical Corporation (St. Louis. Mo.). can be dispersed in 2000 ml ofJet A fuel by stirring at room temperature. 160 ml. of 2,4-pentanedi..e.!..Iadd.o.Iaddend.ne may then be added to the yttrium 2-ethylhexanoate/Jet A mixture and the mixture may be further stirred until allthe yttrium ester is dissolved. This produces a clear fuel coloredsolution containing 3532 ppm yttrium.

We have not identified the exact composition of the resultingester/chelating agent complex. Moreover, we have not determined if thecomposition of the complex varies between one that is fuel soluble andone that is water soluble. We have found, however, that in the presenceof water no yttria precipitate (ordinarily white) forms in either a fuellayer or a water layer. Without the chelating agent, a white yttriaprecipitate is formed.

The inhibitor of the present invention may be added to a hydrocarbonfuel in any conventional way. For example, the inhibitor may be mixedwith the fuel in a storage tank, while the fuel is conveyed to a gasturbine engine, or in any other suitable way. Preferably, the inhibitorwill be thoroughly mixed with the fuel before the fuel is burned tomaximize the extent to which the inhibitor will be available to reactwith V₂ O₅ when it forms in the engine. The amount of inhibitor added tothe fuel should be sufficient to allow a complete reaction between theyttrium in the inhibitor and the V₂ O₅ that forms when the fuel burns.Therefore, the amount of yttrium added to the fuel should at least equalthe stoichiometric amount required for a complete reaction with the V₂O₅. This result can be ensured by providing sufficient yttrium to reactwith all the vanadium in the fuel. Preferably, the amount of yttriumwill be at least 125% of the stoichiometric amount required for acomplete reaction between the yttrium and vanadium. Most preferably, theamount of yttrium will be at least 150% of the stoichiometric amountrequired for a complete reaction between the yttrium and vanadium. Forexample, an amount of inhibitor that provides 550 parts per million(ppm) of yttrium when mixed with a fuel is sufficient to preventvanadium corrosion in a fuel that contains 300 ppm vanadium.

The following examples demonstrate the present invention withoutlimiting the invention's broad scope.

EXAMPLE 1 (Stability of YVO₄ in the presence of Na₂ SO₄)

A yttria (Y₂ O₃) disc was immersed in molten V₂ O₅ and allowed to reactfor approximately two hours to form YVO₄. YVO₄ was confirmed from x-raydiffraction analysis. The YVO₄ -coated disc was covered with sodiumsulfate and exposed in air at 900° C. for two hours. After exposure, thesulfate coated specimen was immersed into hot water and the solutionanalyzed for soluble sodium, vanadium, and sulfate. The results areshown in Table 1. Essentially, all the sodium sulfate applied to thedisc was recovered, indicating little or no reaction between the YVO₄and sodium sulfate. No soluble vanadium was observed. Based upon theseresults, we concluded that YVO₄ is stable in the presence of Na₂ SO₄.

                  TABLE 1    ______________________________________              Amount Applied              to Disk     Amount Recovered from Disk    Element   micromoles  micromoles    ______________________________________    Sodium    7           6.3    Sulfur    3.5         2.9    Vanadium  0           0    ______________________________________

EXAMPLE 2 (Demonstration of YCl₃ as a Corrosion Inhibitor)

A laboratory jet burner rig was modified so that a hypodermic needlecould spray an aqueous solution of vanadyl sulfate (VOSO₄) into the exitnozzle of the burner. The VOSO₄ decomposes to SO₃ and V₂ O₅ at about400° C. to simulate the formation of V₂ O₅ in a full-size gas turbineengine. Nickel-based superalloy specimens were placed downstream of theburner's exit nozzle to simulate turbine components. The concentrationof the VOSO₄ in the burner exhaust and the distance the VOSO₄ traveledwithin the flame before impinging on the superalloy specimens wereexperimentally determined such that all the V₂ O₅ that contacted thespecimens was liquid. The tests were performed under the followingconditions:

    ______________________________________    Fuel:                 Jet A    Fuel Flow Rate:       7.4 kg/hr    Air/Fuel Ratio:       20:1    Test Temperature:     900° C.    Test Duration:        6 hr    ______________________________________

In a first series of tests, the superalloy specimens were exposed onlyto V₂ O₅. Within a few hours, the molten V₂ O₅ severely corroded thespecimens.

In a second series of tests. YCl₃ was added to the solution of VOSO₄.The concentration of yttrium in the solution was exactly that necessaryto react with the vanadium to form YVO₄. In the presence of the yttrium,a thin deposit of YVO₄ formed on the surface of the specimens.Substantially no corrosion was observed on the specimens.

In a last series of tests, Na₂ SO₄ was added to the VOSO₄ /YCl₃ solutionto simulate a sulfidation environment. The Na₂ SO₄ did not alter testresults. As in the second series of test, no corrosion was observed.There was no evidence that the presence of the Na₂ SO₄ prevented orinterfered with the attenuation of V₂ O₅ corrosion by yttria.

These tests showed that yttrium can effectively inhibit vanadium hotcorrosion in the presence of vanadium alone and vanadium plus sulfates.

EXAMPLE 3 (Stability of Ester/Chelate Complex in Water)

A mixture of Jet A fuel and yttrium.sub.(111) 2-ethyl hexanoate (AldrichChemical Corp., St. Louis. Mo.) was formed by adding 2000 ml of Jet Afuel and 50 g of yttrium.sub.(111) 2-ethyl hexanoate to a 4000 ml.flask. After stirring the mixture stirred on a magnetic hot plate (noheat). 160 ml. of 2,4-pentanedi. .e.!..Iadd.o.Iaddend.ne was added tothe flask. This mixture was stirred until all the yttrium ester wasdissolved, producing a clear fuel colored solution. The solutioncontained 3532 ppm yttrium. Adding water to the flask formed two clearlayers one fuel, the other water. Both layers contained yttrium. Thedistribution of yttrium between the two layers was related to the volumeof the two fluids. No yttria precipitate (ordinarily white) was observedin either the fuel layer or water layer. Previously, such a precipitatewas observed without the chelating agent.

A second water extraction showed that very little (˜1%) of the yttriumcomplex remaining in the fuel went into the water layer. As before,there was no white yttria precipitate. This result indicated that thereare several different ester/chelate species formed during the reaction,some water soluble and some fuel soluble. All species appeared to bestable in water.

EXAMPLE 4 (Demonstration of Ester/Chelate Complex as a CorrosionInhibitor)

Example 2 was repeated with the yttrium ester/chelate complex formed inExample 3 substituted for the YCl₃. For several of the tests, sodium wasintroduced into the combustor in the form of sodium sulfate. The resultsof these tests are shown in Table II.

                  TABLE II    ______________________________________                  Corro-            Inhibi-                  dent              tor                  Concen-           Concen-         Corro-   tration           tration    Test dent     ppm       Inhibitor                                    ppm     Comments    ______________________________________    1    none     --        ester/chelate                                    550     no deposit                            complex    2    vanadium 300       none    --      corrosion    3    sodium    33       none    --      corrosion    4    sodium   100       none    --      corrosion    5    vanadium 300       ester/chelate                                    550     no                            complex         corrosion    6    vanadium 300       ester/chelate                                    550     no         sodium    33       complex         corrosion    7    vanadium 300       ester/chelate                                    550     no         sodium   100       complex         corrosion    ______________________________________

In test 1 (inhibitor, no corrodent), the inhibitor formed an extremelythin, whitish, non-adherent film on the surface of the specimens.

In tests 2-4 (corrodent, no inhibitor), a thick, non-adherent purplescale, which exfoliated during cool-down from test to room temperature,formed.

In tests 5-7 (corrodent, inhibitor), a thin, grayish, non-adherent filmcovered the surfaces of the specimens. Visually ally the surfacesappeared free of corrosion. This was confirmed from metallographicalstudies.

These tests showed that yttrium can effectively inhibit vanadium hotcorrosion in the presence of vanadium alone, sodium alone, and vanadiumplus sodium.

The results of the examples, particularly Examples 2 and 4 show that thevanadium corrosion inhibitor of the present invention provides severalbenefits over the prior art. Unlike the prior art magnesium-basedinhibitors, the yttrium-based inhibitors of the present invention areeffective with vanadium alone and in the presence of sodium andsulfates. In addition, the yttrium-based inhibitors produce a reactionproduct. YVO₄ (melting point>1800° C.). with a higher melting point thanthe reaction product of magnesium-based inhibitors. Mg₃ (VO₄)₂ (meltingpoint=1150° C.). As a result, the corrosion inhibitors of the presentinvention can be used for higher temperature applications that the priorart corrosion inhibitors.

We claim:
 1. A fuel mixture comprising a hydrocarbon fuel and a yttriumester/chelate complex, wherein when the hydrocarbon fuel is burned, V₂O₅ is a by-product, and wherein the concentration of the yttrium complexin the mixture provides at least a stoichiometric amount of yttrium fora substantially complete reaction between the yttrium and V₂ O₅ wherebythe yttrium and V₂ O₅ react to form YVO₄.
 2. The mixture of claim 1,wherein the concentration of the yttrium complex in the mixture providesat least 125% of the stoichiometric amount of yttrium required for asubstantially complete reaction between the yttrium and vanadium.
 3. Themixture of claim 1, wherein the yttrium ester comprises at least fourcarbon atoms and the chelating agent is hydrocarbon fuel soluble andthat includes 2,4-pentanedi. .e.!..Iadd.o.Iaddend.ne and the complex hasa molar ratio of 2,4-pentanedi. .e.!..Iadd.o.Iaddend.ne to yttrium of upto 5:1.
 4. The mixture of claim 3, wherein the yttrium ester comprisesfour to twelve carbon atoms.
 5. The mixture of claim 3, wherein theyttrium ester is selected from the group consisting of yttrium octonateand yttrium 2-ethyl hexanoate.
 6. The mixture of claim 3, wherein themolar ratio of 2,4-pentanedi. .e.!..Iadd.o.Iaddend.ne to yttrium is 2:1to 3:1.
 7. The mixture of claim 3, wherein the yttrium ester is selectedfrom the group consisting of yttrium octonate and yttrium 2-ethylhexanoate and the molar ratio of 2,4-pentanedi. .e.!..Iadd.o.Iaddend.neto yttrium is 2:1 to 3:1.
 8. A hydrocarbon fuel soluble, water stablevanadium corrosion inhibitor yttrium ester chelate complex, comprising ayttrium ester having at least four carbon atoms and a hydrocarbon fuelsoluble chelating agent that includes 2,4-pentanedi..e.!..Iadd.o.Iaddend.ne wherein the complex has a molar ratio of2,4-pentanedi. .e.!..Iadd.o.Iaddend.ne to yttrium of up to 5:1.
 9. Theinhibitor of claim 8, wherein the yttrium ester comprises four to twelvecarbon atoms.
 10. The inhibitor of claim 8, wherein the yttrium ester isselected from the group consisting of yttrium octonate and yttrium2-ethyl hexanoate.
 11. The inhibitor of claim 8, wherein the molar ratioof 2,4-pentanedi. .e.!..Iadd.o.Iaddend.ne to yttrium is 2:1 to 3:1. 12.The mixture of claim 9, wherein the molar ratio of 2,4-pentanedi..e.!..Iadd.o.Iaddend.ne to yttrium is 2:1 to 3:1.
 13. The mixture ofclaim 10, wherein the molar ratio of 2,4-pentanedi..e.!..Iadd.o.Iaddend.ne to yttrium is 2:1 to 3:1.